Anti-reflection film and process for preparation thereof

ABSTRACT

This invention provides an anti-reflection film for use in various displays which prevents the reflection of light on the surface and enables necessary visual information to be clearly discerned. The anti-reflection film has a hard coat layer  4 , an intermediate refractive index layer  3 , a high refractive index layer  2  and a low refractive index layer  1  formed in this sequence on a transparent base film  5 , such that the refractive indices of the adjacent layers satisfy the relationship 2.20&gt;refractive index of the high refractive index layer&gt;refractive index of the intermediate refractive index layer&gt;refractive index of the low refractive index layer&gt;1.40.

BACKGROUND OF THE INVENTION

[0001] The present invention relates to a film having optical functionssuch as anti-glare properties. More specifically, the invention relatesto a film with excellent optical characteristics which is suitable as ananti-reflection film on the surface of various displays of wordprocessors, computers and TV sets, polarizing plates for use in liquidcrystal display devices, lenses of sunglasses composed of transparentplastics, lenses of vision-correcting eyeglasses, optical lenses such ascamera finder lenses, covers for various gauges, and window glasses ofautomobiles and electric trains.

[0002] Transparent base plates of glass, plastic or the like are usedfor displays of curve mirrors, rear view mirrors, goggles, windowglasses, displays for personal computers and word processors, andvarious other displays for commercial use. One may see objects orrecognizes visual information, such as characters or graphics, throughthese transparent base plates, or may observe images from a reflectionlayer through the transparent base plate of the mirror. In so doing, onemay feel it difficult to discern the necessary visual informationlocated in the transparent base plate, because the surface of thetransparent base plate reflects light.

[0003] Techniques for preventing the reflection of light include amethod of coating an anti-reflection coating on the surface of a glassor plastic material, a method of providing a super thin film of MgF₂ orthe like or a vacuum deposited metal film about 0.1 μm thick on thesurface of a transparent base plate of glass or the like, a method ofcoating an ionizing radiation curing resin on the surface of a plasticlens and forming a film of SiO_(X) or MgF₂ on the coating by vacuumdeposition, and a method of further forming a coating with a lowrefractive index on a cured film of an ionizing radiation curing resin.

[0004] The above-mentioned thin film of MgF₂ about 0.1 μm thick formedon glass will be described in further detail. This thin film as ananti-reflection film is required to prevent reflection of lightcompletely and allow 100% transmission of light when incident lightfalls vertically on the thin film in the air. With a specific wavelengthdesignated as λ₀, the refractive index of the anti-reflection film forthis wavelength as n₀, the thickness of the anti-reflection film as h,and the refractive index of the base plate as n₂, the relations of thefollowing Equations 1 and 2 must hold to fulfill the above requirements,as have been already known (Science Library, Physics=9 “Optics”, pp.70-72, 1980, Science Ltd.): $\begin{matrix}{n_{0} = \left( n_{2} \right)^{1/2}} & \text{(Equation~~1)} \\{{n_{0}h} = {\lambda_{0}/4}} & \text{(Equation~~2)}\end{matrix}$

[0005] The refractive index of glass n₂=1.5, the refractive index ofMgF₂ n₀=1.38, and the wavelength of incident light λ₀=5500 Å (reference)are known. Substituting these values into Equation 2 yields about 0.1 μmas the optimal thickness h of the anti-reflection film.

[0006] Equation 1 tells that an effective way of preventing reflectionof light 100% is to select a material in which the refractive index of acoating on the upper layer side is close to the square root of therefractive index of the lower layer laid under the coating.

DISCLOSURE OF THE INVENTION

[0007] An object of the present invention is to provide ananti-reflection film for use in a display in which the surface of atransparent base plate prevents the reflection of light and transmitsnecessary visual information inside the transparent base plate, andenables an observer to clearly discern the visual information, whenseeing objects or visual information, such as characters or graphics,through the transparent base plate, or observing an image from areflection layer through the transparent base plate of a mirror.

[0008] The invention for attaining this object, as shown in FIG. 1 or 2,resides in an anti-reflection film 10 having an intermediate refractiveindex layer 3, a high refractive index layer 2 and a low refractiveindex layer 1 formed in this sequence on a transparent base film 5 via ahard coat layer 4, the anti-reflection film 10 comprising:

[0009] the low refractive index layer 1 comprising an SiO_(X) layer;

[0010] the intermediate refractive index layer 3 constituted by acoating of a composition comprising a binder and ultrafine particleshaving a refractive index of 1.5 or more; and

[0011] the high refractive index layer 2 having electric conductivity;and

[0012] the anti-reflection film 10 having:

[0013] the relationship: 2.20>refractive index of the high refractiveindex layer>refractive index of the intermediate refractive indexlayer>refractive index of the low refractive index layer>1.40;

[0014] the thickness of each refractive index layer being 80 to 110 nmfor the low refractive index layer, 30 to 110 nm for the high refractiveindex layer, and 50 to 100 nm for the intermediate refractive indexlayer; and

[0015] an optical film thickness D not larger than the wavelength ofvisible light (D=n·d where n is the refractive index of the intermediaterefractive index layer and d is the thickness of the intermediaterefractive index layer).

[0016] In the present invention, it is preferred that theanti-reflection film 10 is such that the hard coat layer 4 hasirregularities on its surface in contact with the intermediaterefractive index layer 3, and the hard coat layer 4 is provided on thetransparent base film 5 directly or via a primer layer 7 and/or anadhesive layer 9, as illustrated in FIG. 6.

[0017] Preferably, the anti-reflection film 10 is such that theintermediate refractive index layer is composed of 0.1 to 20 parts byweight of a mat material based on one part by weight of a thermosettingresin and/or an ionizing radiation curing resin, the mat material beingselected from fine particles of one or more kinds selected from thegroup consisting of ultrafine particles of ZnO, TiO₂, CeO₂, Sb₂O₅, SnO₂,ITO, Y₂O₃, La₂O₃, Al₂O₃, Hf₂O₃ and ZrO₂.

[0018] Preferably, the anti-reflection film 10 is such that the highrefractive index layer and the low refractive index layer are each alayer provided by vacuum coating.

[0019] Preferably, the anti-reflection film 10 is such that the lowrefractive index layer is formed by plasma CVD involving the dischargeof the starting gas of an organosiloxane, and the undecomposedorganosiloxane remains in an amount of 0.1 to 0.2 part based on theSiO_(X).

[0020] Furthermore, an antifouling layer may be formed on the lowrefractive index layer.

[0021] A first process for preparation of the anti-reflection film ofthe present invention is as follows:

[0022] As shown in FIG. 3, an uncured hard coat layer 46 of the curingreaction type is provided on a transparent base film 5. Then, an uncuredintermediate refractive index layer 36 comprising a compositioncontaining a binder and fine particles having a higher refractive indexthan the refractive index of the binder is coated on the transparentbase film.

[0023] A laminate having a finely irregular, matted shaped film 6laminated and shaped on the uncured hard coat layer and intermediaterefractive index layer (see FIG. 3A) is heat-treated and/or ionizingradiation treated to cure the hard coat layer and intermediaterefractive index layer.

[0024] From the cured laminate, the shaped film 6H is stripped off toform an intermediate refractive index layer 3 having irregularities onthe surface of a hard coat layer 4 as illustrated in FIG. 3B.

[0025] On the cured intermediate refractive index layer 3 havingirregularities, a high refractive index layer 2 is formed by vacuumdeposition or sputtering. Further, a low refractive index layer 1comprising an SiO_(X) layer is formed by vacuum deposition, sputteringor plasma CVD to constitute an anti-reflection film 10. This is shown inFIG. 3C.

[0026] A second process for preparation of the anti-reflection film ofthe invention is as follows:

[0027] A matted shaped film 6 having irregularities on the surface iscoated with an uncured intermediate refractive index layer 36 comprisinga composition containing a binder and fine particles having a higherrefractive index than the refractive index of the binder. To the uncuredintermediate refractive index layer, an uncured hard coat layer 46provided on a transparent base film 5 is laminated as shown in FIG. 4A.

[0028] The resulting laminate is heat-treated and/or ionizing radiationtreated to cure the intermediate refractive index layer and hard coatlayer. From the cured laminate, the shaped film 6H is stripped off toform an intermediate refractive index layer 3 having irregularities onthe surface of a hard coat layer 4 (see FIG. 4B).

[0029] Then, as shown in FIG. 4C, a high refractive index layer 2 and alow refractive index layer 1 are laminated and formed in the same manneras in the first preparation process. If desired, an antifouling coatlayer 42 may be formed on the low refractive index layer.

[0030] A third process for preparation of the anti-reflection film ofthe invention is as follows:

[0031] As shown in FIG. 5A, a shaped film 6 is coated with an uncuredintermediate refractive index layer containing a binder and fineparticles having a higher refractive index than the refractive index ofthe binder, and an uncured hard coat layer. Then, the uncured layers arecured.

[0032] Separately, a transparent base film is coated with a reactiveadhesive layer 9. On the uncured surface of the reactive adhesive layer9, the cured intermediate refractive index layer is laminated. Theresulting laminate is heat-treated and/or ionizing radiation treated tocure the adhesive layer to prepare a laminate as shown in FIG. 5B.

[0033] From the cured laminate, the shaped film 6H is stripped off toform an intermediate refractive index layer 3 on a transparent base film5 via the adhesive layer 9 and the hard coat layer 4.

[0034] Then, as shown in FIG. 5C, a high refractive index layer 2 and alow refractive index layer 1 are laminated in the same manner as in thefirst preparation process to constitute an anti-reflection film 10.

BRIEF DESCRIPTION OF THE DRAWINGS

[0035]FIG. 1 is a sectional view showing the basic layered structure ofthe anti-reflection film of the present invention;

[0036]FIG. 2 is a sectional view showing a constitution in which anintermediate refractive index layer having irregularities is added tothe anti-reflection film of the present invention;

[0037]FIGS. 3A, 3B and 3C are sectional schematic views showing thesteps of the first process for preparation according to the presentinvention;

[0038]FIGS. 4A, 4B and 4C are sectional schematic views showing thesteps of the second process for preparation according to the presentinvention;

[0039]FIGS. 5A, 5B and 5C are sectional schematic views showing thesteps of the third process for preparation according to the presentinvention;

[0040]FIG. 6 is a sectional schematic view showing another constitutionof the present invention;

[0041]FIG. 7 is a sectional schematic view showing the constitution of aComparative Example;

[0042]FIG. 8 is a sectional schematic view showing the constitution ofanother Comparative Example; and

[0043]FIG. 9 is a view showing the reflectivity spectrum in the visiblelight region of some of the anti-reflection films of the Examples of thepresent invention and the Comparative Examples.

BEST MODE FOR CARRYING OUT THE INVENTION

[0044] Preferred embodiments of the present invention will now bedescribed with reference to the accompanying drawings.

[0045] As shown in FIG. 1 or 2, an anti-reflection film 10 of thepresent invention has an intermediate refractive index layer (firstlayer) 3, a high refractive index layer (second layer) 2 and a lowrefractive index layer (third layer) 1 formed in this sequence on onesurface of a transparent base film 5 via a hard coat layer 4 in a mirrorshape or given irregularities.

[0046] The anti-reflection film 10 is constituted such that

[0047] the low refractive index layer 1 comprises an SiO_(X) layer;

[0048] the intermediate refractive index layer 3 is constituted on ahard coat layer 4 with irregularities by coating a paint comprising abinder and ultrafine particles having a refractive index of 1.5 or more;and

[0049] the high refractive index layer 2 has electric conductivity andelectromagnetic shielding properties;

[0050] the refractive indices of the adjacent refractive index layers ofthe respective layers satisfy the relationship: 2.20>refractive index ofthe high refractive index layer>refractive index of the intermediaterefractive index layer (or the intermediate refractive index layerhaving irregularities)>refractive index of the low refractive indexlayer>1.40;

[0051] the thicknesses of the respective refractive index layers are 80to 110 nm for the low refractive index layer 1, 30 to 110 nm for thehigh refractive index layer 2, and 50 to 100 nm for the intermediaterefractive index layer 3; and

[0052] an optical film thickness D calculated from the equation D=n·d(wherein n=refractive index of the intermediate refractive index layer,and d=thickness of the intermediate refractive index layer) is notlarger than the wavelength of visible light.

[0053] Preferably, the anti-reflection film 10 is such that the hardcoat layer 4 has irregularities on its surface in contact with theintermediate refractive index layer 3, and the hard coat layer 4 isprovided on the transparent base film 5 directly or via a primer layer 7as shown in FIG. 6, or via an adhesive layer 9 as shown in FIG. 5, andthe low refractive index layer 1 is provided with an antifouling layer42.

[0054] Preferably, the anti-reflection film 10 is such that theintermediate refractive index layer 3 is composed of 0.1 to 20 parts byweight of a mat material based on one part by weight of a thermosettingresin and/or an ionizing radiation curing resin, the mat material beingselected from fine particles of one or more kinds selected from thegroup consisting of ultrafine particles of ZnO (refractive index 1.90;the values indicated below represent refractive indices), TiO₂(2.3-2.7), CeO₂ (1.95), Sb₂O₅ (1.71), ITO (1.95), Y₂O₃ (1.87), La₂O₃(1.95), ZrO₂ (2.05), and Al₂O₃ (1.63). The ultrafine particlespreferably have a higher refractive index than that of the binder of theintermediate refractive index layer, and have a refractive index of 1.5or more. The average particle size of the ultrafine particles ispreferably 5 to 50 nm, and more preferably 5 to 10 nm.

[0055] Preferably, the high refractive index layer 2 and the lowrefractive index layer 1 are each a layer provided by vacuum coating.

[0056] Preferably, the low refractive index layer 1 is formed by plasmaCVD involving the discharge of the starting gas of an organosiloxane,and the undecomposed organosiloxane remains in the SiO_(X) layer.

[0057] Furthermore, an antifouling layer 42 as shown in FIG. 6 may beformed on the low refractive index layer 1.

[0058] The transparent base sheet of the present invention is formedfrom a ceramic material such as glass, or a transparent stretched orunstretched plastic film.

[0059] Besides ordinary optical glass, thermoplastic resins can be used,such as polyester, polyamide, polyimide, polypropylene,polymethylpentene, polyvinyl chloride, polyvinyl acetal, polymethylmethacrylate, polycarbonate, and polyurethane.

[0060] On the transparent base film, a hard coat layer having tinyirregularities may be provided directly or through a primer layer formaking the adhesion of the hard coat layer firm. On the hard coat layer,an intermediate refractive index layer 3 as shown in FIG. 2 may beprovided, and other refractive index layer may be further provided.

[0061] The intermediate refractive index layer 3 is lower in refractiveindex than the high refractive index layer 2, and higher in refractiveindex than the low refractive index layer 1, hard coat layer 4 and/ortransparent base film 5.

[0062] The intermediate refractive index layer 3 is preferably providedon the base film 5 by coating a composition comprising a binder andultrafine particles of a metal oxide as a mat material selected fromfine particles of one or more kinds selected from the group consistingof ZnO, TiO₂, CeO₂ (refractive index 1.95), Sb₂O₅, SnO₂, ITO, Y₂O₃,La₂O₃, ZrO₂ (refractive index 2.05), Al₂O₃ and Hf₂O₃.

[0063] The intermediate refractive index layer 3 is formed, as shown inFIG. 3, by coating an uncured hard coat layer 46 on the transparent basefilm 5, further coating an uncured intermediate refractive index layer36, laminating these uncured layers to a shaped film 6, heating and/orionizing radiating treating the laminate to cure the layers, andstripping the shaped film 6 off.

[0064] Furthermore, as shown in FIG. 4, the intermediate refractiveindex layer 3 can be constituted by a transfer method which comprisesproviding an uncured intermediate refractive index layer 36 and anuncured hard coat layer 46 on a shaped film 6 having irregularities,providing an adhesive layer 9, if desired, on the transparent base film,laminating these layers together, and curing and shaping the laminate.

[0065] The ratio of the ultrafine particles to the binder (weight ratio)in the intermediate refractive index layer is preferably 1-20 (ultrafineparticles):1 (binder). If this ratio is less than 1:1, the effect ofanti-reflection decreases. At a ratio of more than 20:1, the adhesion ofthe ultrafine particles declines, and the ultrafine particlesincreasingly tend to fall off.

[0066] The irregularities for providing the intermediate refractiveindex layer of the invention may be provided for the shaped hard coatlayer 4, but the same function may be imparted by shaping the adhesivelayer 9 or primer layer 7, the layer on the transparent base film, intoan irregular form. The irregularities of the hard coat layer 4 are indirect contact with the intermediate refractive index layer 3, and therefractive index of the hard coat layer 4 is smaller than the refractiveindex of the intermediate refractive index layer 3.

[0067] The reactive resin that satisfies the foregoing requirements andserves to form the intermediate refractive index layer or the hard coatlayer preferably includes, for example, those containing a relativelylarge amount of a compound having an acrylate type functional group,such as relatively low molecular weight polyester, polyether, acrylicresin, epoxy resin, polyurethane, alkyd resin, spiroacetal resin,polybutadiene, polythiolpolyene resin, an oligomer or prepolymer of(meth)acrylate (in this specification, acrylate and methacrylate arecollectively expressed as (meth)acrylate) of a polyfunctional compoundsuch as polyhydric alcohol, and a monofunctional monomer such as ethyl(meth)acrylate, ethylhexyl (meth)acrylate, styrene, vinyltoluene orN-vinylpyrrolidone which is a reactive diluent, and a multifunctionalmonomer such as trimethylolpropane tri(meth)acrylate, hexanediol(meth)acrylate, tripropylene glycol di(meth)acrylate, diethylene glycoldi(meth)acrylate, pentaerythritol tri(meth)acrylate, dipentaerythritolhexa(meth)acrylate, 1,6-hexanediol di(meth)acrylate, or neopentyl glycoldi(meth)acrylate.

[0068] When the ionizing radiation curing resin is used as anultraviolet curing resin, it is preferred to incorporate therein aphotopolymerization initiator such as acetophenone, benzophenone,Michler's benzoyl benzoate, α-amyloxime ester, or thioxanthone, and aphotosensitizer such as n-butylamine, triethylamine, ortri-n-butylphosphine.

[0069] The ionizing radiation curing resin may further contain thefollowing reactive organosilicon compound:

[0070] A compound of the formula R_(m)Si(OR′)_(n) where R and R′ eachdenote an alkyl group having 1 to 10 carbon atoms, m+n=4, and m and neach denote an integer. Examples of the compound are tetramethoxysilane,tetraethoxysilane, tetra-iso-propoxysilane, tetra-n-propoxysilane,tetra-n-butoxysilane, tetra-sec-butoxysilane, tetra-tert-butoxysilane,tetrapentaethoxysilane, tetrapenta-iso-propoxysilane,tetrapenta-n-propoxysilane, tetrapenta-n-butoxysilane,tetrapenta-sec-butoxysilane, tetrapenta-tert-butoxysilane,methyltrimethoxysilane, methyltriethoxysilane, methyltripropoxysilane,methyltributoxysilane, dimethyldimethoxysilane, dimethyldiethoxysilane,dimethylethoxysilane, dimethylmethoxysilane, dimethylpropoxysilane,dimethylbutoxysilane, methyldimethoxysilane, methyldiethoxysilane, andhexyltrimethoxysilane.

[0071] The thickness of the hard coat layer 4 is preferably 0.5 to 6 μm,more preferably 3 μm or more. If the thickness is less than 0.5 μm, itcannot maintain the hardness of the intermediate refractive index layer,the high refractive index layer and the low refractive index layerformed on the transparent base film. If its thickness is more than 3 μm,satisfactory hardness can be maintained, and hardness performance can beimparted to the anti-reflection film.

[0072] Making the hard coat layer thicker than required would impair theflexibility of the anti-reflection film, and take time for curing,imposing restrictions on the productivity and cost.

[0073] The term “hardness performance” or “hard coat” as used hereinrefers to hardness of the grade H or higher according to the pencilhardness test described in JISK5400.

[0074] The material for use in the high refractive index layer 2 of theinvention should desirably be one higher in refractive index than thebinder in the intermediate refractive index layer, and having arefractive index of 1.5 or more. This material may be the same as thefine particle material used in the intermediate refractive index layer.

[0075] One or more materials selected from the above-described compoundsare used to form the high refractive index layer by vacuum deposition orsputtering. The high refractive index layer is given the highestrefractive index of the refractive indices of the respective layers ofthe invention so that the thickness d of the intermediate refractiveindex layer will be 80 to 110 nm, and its refractive index will be 1.90to 2.10. The product of the refractive index n and the thickness d(i.e., the optical thickness D) is adjusted to not larger than thewavelength of visible light so that the reflection of light can beprevented and the transmission of visible light can be optimized.

[0076] The high refractive index layer is preferably composed of asputter film of ITO, and its surface resistance is desirably 10³Ω/¤ orless.

[0077] In this case, the binder of the intermediate refractive indexlayer is preferably formed of a thermosetting and/or ionizing radiationcuring organosilicon compound. Thus, the adhesion of the intermediaterefractive index layer to the above-mentioned ITO layer can be increasedfurther.

[0078] The ultrafine particles of the intermediate refractive indexlayer, particularly preferably, comprise ZrO₂ particles to impart betterdurability.

[0079] The low refractive index layer of the invention comprises SiO_(X)(x=1.5−4.0), and can be formed by CVD, or preferably by plasma CVD usingan organosiloxane as the starting gas under conditions under which noother inorganic vacuum deposition source exists. The vacuum depositedfilm is maintained at as low a temperature as possible.

[0080] The SiO_(X) layer (low refractive index layer) of the inventionis adapted to contain the undecomposed organosiloxane and to have carbonremaining at a ratio of 0.1-0.2 to silicon. Thus, the effect ofmaintaining the flexibility and adhesion of SiO_(X) can be enhancedfurther.

[0081] The thus formed low refractive index layer comprises the SiO_(X)layer with a contact angle of the surface to water of from 40 to 180degrees. Hence, this layer is also effective in preventing thedeposition of dust.

[0082] A polarizing plate having the so constituted anti-reflection film10 laminated on a polarizer, or a cathode-ray tube with theanti-reflection film 10 bonded onto the surface gives a sharp image andis reflection-free.

[0083] A liquid crystal display device with the polarizing platebuilt-in shows a sharp image free from reflected light.

[0084] The present invention will now be described in more detail byreference to Examples.

EXAMPLE 1

[0085] On one surface of a 50 μm thick biaxially stretched polyethyleneterephthalate film (Lumirror T-60#50, TORAY INDUSTRIES, INC.) as ashaped film 6 as shown in FIG. 4, ZrO₂ fine particle coating solutionNo. 1275 [a coating solution comprising 0.3 part by weight of a binder(an ionizing radiation curing organosilicon compound) per 100 parts byweight of ZrO₂ fine particles; Sumitomo Osaka Cement Co., Ltd.] wascoated to a thickness of 57 nm (dry thickness; the same holds in thefollowing description) by means of a wire bar to form an uncuredintermediate refractive index layer 36 (refractive index 1.74).

[0086] Separately, an ultraviolet curing resin (PET-D31, DAINICHISEIKACOLOUR & CHEMICALS MFG. CO., LTD.) was coated on a 188 μm thick PET film(A-4350#188, TOYOBO, CO., LTD.) as a transparent base film 5 to athickness of 6 μm, followed by drying the solvent component, to form anuncured hard coat layer 46.

[0087] Then, the uncured intermediate refractive index layer 36 providedon the shaped film 6, and the uncured hard coat layer 46 provided on thetransparent base film 5 were laminated and pressure-bonded together incontact with each other. Then, the laminate was irradiated withultraviolet rays at a dose of 480 mJ (10 m/min) to cure the uncuredintermediate refractive index layer 36 and hard coat layer 46 to form anintermediate refractive index layer 3 and a hard coat layer 4. Then, theshaped film 6 was peeled off.

[0088] As shown in FIG. 4B, the transparent base film 5 cleared of thepeeled shaped film 6H had the hard coat layer 4 and the intermediaterefractive index layer 3 superimposed thereon with the fine particles ofthe intermediate refractive index layer 3 embedded in and transferred tothe surface of the hard coat layer 4.

[0089] Further, as shown in FIG. 4C, ITO sputtering (refractive index2.0) was performed on the side of the intermediate refractive indexlayer 3 under the conditions, a vacuum of 5×10⁻⁶ torr, a base platetemperature of room temperature, argon of 100 scc/min, oxygen of 5scc/min, and a deposit rate of 1.6 Å/s, to form a high refractive indexlayer 2 with a thickness of 105 nm.

[0090] On the high refractive index layer 2, SiO₂ (refractive index1.46) was vacuum deposited under the conditions, a vacuum of 5×10⁻⁶torr, a base plate temperature of room temperature, and a deposit rateof 26 Å/s, to form a low refractive index layer 1 with a thickness of 85nm.

[0091] On the low refractive index layer 1 side, fluorine surfactantFC-772 (a product of 3M) was further coated to a thickness of 2 nm bymeans of a wire bar to complete an anti-reflection film 10 of Example 1.

EXAMPLE 2

[0092] On one surface of MC-19 (a product of Reiko Co., Ltd.) as a 50 μmthick shaped film 6 surface treated with acrylic melamine resin, asshown in FIG. 5, ZrO₂ fine particle coating solution No. 1221 [a coatingsolution comprising 0.3 part by weight of a binder (an ionizingradiation curing organosilicon compound) per 100 parts by weight of Zro₂fine particles; Sumitomo Osaka Cement Co., Ltd.] was coated to athickness of 57 nm by means of a wire bar to form an uncuredintermediate refractive index layer 36 (refractive index 1.74).

[0093] On the intermediate refractive index layer 36 side, anultraviolet curing resin (PET-D31, DAINICHISEIKA COLOUR & CHEMICALS MFG.CO., LTD.) was coated to a thickness of 8 μm, followed by drying thesolvent component, to form an uncured hard coat layer 46.

[0094] Then, the uncured intermediate refractive index layer 36 and theuncured hard coat layer 46 were irradiated with ultraviolet rays at adose of 480 mJ (10 m/min) to cure the uncured intermediate refractiveindex layer and hard coat layer to provide an intermediate refractiveindex layer 3 and a hard coat layer 4 on the shaped film 6.

[0095] As a result, the fine particles of the intermediate refractiveindex layer 3 were embedded in and transferred to the surface of thetransparent cured resin layer 4, and the hard coat layer 4 and theintermediate refractive index layer 3 were superimposed on thetransparent shaped film 6.

[0096] On the hard coat layer 4 side, a urethane-derived two-componentsetting adhesive LX-660/KW75=4/1 (a product of DIC) was coated to athickness of 10 μm by wire bar coating to form an uncured adhesive layer43. On the layer 43, a triacetyl cellulose film FT-UV80 (a product ofFuji Photo Film Co., Ltd.) was superimposed as a transparent base film5. The laminate was aged for 7 days at 40° C. to complete the curing ofthe adhesive, forming a transparent cured adhesive layer 9, followed bystripping off the shaped film 6H. On the surface of the intermediaterefractive index layer 3 deprived of the peeled shaped film 6H, ITOsputtering was performed under the same conditions as in Example 1 toform a high refractive index layer 2. SiO₂ was further superimposed onthe high refractive index layer 2 by plasma CVD to complete ananti-reflection film 10 of Example 2.

EXAMPLE 3

[0097] On one surface of a 188 μm thick biaxially stretched polyethyleneterephthalate film T-PET (A-4350, TOYOBO CO., LTD.) as a transparentbase film 5 as shown in FIG. 3, the same uncured hard coat layer 46 asused in Example 1 was applied to a thickness of 8 μm. Also, a coatingsolution comprising 0.4 part by weight of a binder per 100 parts byweight of TiO₂ fine particles (the coating solution produced by SumitomoOsaka Cement Co., Ltd.] was coated to a thickness of 57 nm by means of awire bar to form an uncured intermediate refractive index layer 36(refractive index 1.74).

[0098] On the surface of the uncured intermediate refractive index layer36, the same shaped film 6 as used in Example 1 was superimposed,following by curing the laminate.

[0099] Thus, a hard coat layer 4 and an intermediate refractive indexlayer 3 having irregularities were formed in the same manner as inExample 1, followed by stripping off a strippable shaped film 6H.

[0100] On the side of the intermediate refractive index layer 3, a 105nm thick, high refractive index layer 2 by ITO sputtering (refractiveindex 2.0), and a 85 nm thick, low refractive index layer 1 of SiO₂(refractive index 1.46) were formed.

[0101] On the low refractive index layer 1 side, the same fluorinesurfactant FC-772 as used in Example 1 was further coated to a thicknessof 2 nm to complete an anti-reflection film 10 of Example 3 that usedTiO₂ instead of ZrO₂ in Example 1.

COMPARATIVE EXAMPLE 1

[0102] As shown in FIG. 7, a hard coat layer 45 with a thickness of 8 μmwas provided on a 188 μm thick PET film (A-4350#188, TOYOBO, CO., LTD.)as a transparent base film 5. Further, MgO (refractive index 1.72) wasvacuum deposited to a thickness of 57 nm to provide a refracting layer26. Then, a refracting layer 27 by ITO sputtering and a refracting layer28 by vacuum deposition of SiO₂ were provided in the same manner as inExample 1 to complete an anti-reflection film 10H of a ComparativeExample.

COMPARATIVE EXAMPLE 2

[0103] An anti-reflection film of Comparative Example 2 was prepared inthe same manner as in Comparative Example 1, except that the secondrefracting layer was formed by vacuum deposition of TiO₂ instead of ITOsputtering.

[0104] A hard coat layer 45 with a thickness of 8 μm was provided on onesurface of a base film 5. Further, MgO (refractive index 1.72) wasvacuum deposited to a thickness of 57 nm to provide a refracting layer26. Then, a highly refracting layer 27 (film thickness 100 nm) by vacuumdeposition of TiO₂, and a refracting layer 28 (film thickness 85 nm) byvacuum deposition of SiO₂ were provided to complete an anti-reflectionfilm 10H of a Comparative Example.

COMPARATIVE EXAMPLE 3

[0105] As shown in FIG. 8, a hard coat layer 45 with a thickness of 8 μmwas provided on a transparent base film 5 in the same manner as inComparative Example 1.

[0106] Further, ITO sputtering (refractive index 2.0) was performed onthe side of the hard coat layer 45 under the conditions, a vacuum of5×10⁻⁶ torr, a base plate temperature of room temperature, argon of 100scc/min, oxygen of 5 scc/min, and a deposit rate of 1.6 Å/s, to form afirst refractive index layer 26 with a thickness of 25 nm.

[0107] On the first refractive index layer 26, SiO₂ (refractive index1.43) was vacuum deposited under the conditions, a vacuum of 5×10⁻⁶torr, a base plate temperature of room temperature, and a deposit rateof 2 Å/s, to form a second refractive index layer 27 with a thickness of20 nm.

[0108] Further, ITO sputtering was performed on the side of the secondrefractive index layer 27 under the conditions, a vacuum of 5×10⁻⁶ torr,a base plate temperature of room temperature, argon of 100 scc/min,oxygen of 5 scc/min, and a deposit rate of 1.6 Å/s, to form a thirdrefractive index layer 28 with a thickness of 120 nm.

[0109] On the third refractive index layer 28, vacuum deposition of SiO₂was performed under the conditions, a vacuum of 5×10⁻⁶ torr, a baseplate temperature of room temperature, and a deposit rate of 2 Å/s, toform a fourth refractive index layer 29 with a thickness of 100 nm,thereby completing an anti-reflection film of Comparative Example 3.

EXAMPLE 4

[0110] An anti-reflection film was prepared in the same manner as inExample 1, except that

[0111] the film thickness of the intermediate refractive index layer(ZrO₂:n=1.74)=90 nm,

[0112] the film thickness of the high refractive index layer(ITO:n=2.0)=40 nm, and

[0113] the film thickness of the low refractive index layer(SiO₂:n=1.46)=100 nm.

COMPARATIVE EXAMPLE 4

[0114] Although not shown, a 7 μm thick hard coat layer 45 as used inComparative Example 4 was provided on a PET film 5 in the same manner asin Comparative Example 4. Further, ITO and SiO2 were vacuum deposited inthis order to optical film thicknesses of (λ/4−λ/4), i.e., depositedlaminated film thicknesses 69 nm and 94 nm, respectively, as tworefracting layers consisting of a first refracting layer and a secondrefracting layer. Thus, an anti-reflection film of Comparative Example 4was prepared.

[0115] The samples obtained in the Examples and Comparative Exampleswere measured for the spectral drawings of anti-reflection films toinvestigate the low reflectivity region less than 1%. The samples werealso measured for surface characteristics (surface resistance, measuredby the four-terminal method; contact angle of surface, measured by ModelG1, a contact angle measuring instrument of Elmer; humidity resistancetest, a test for visual evaluation of a change in appearance after thesample is allowed to stand for 48 hours in an environment of 50° C. andrelative humidity of 95%; and coefficient of dynamic friction).

[0116] The results of measurement are shown in FIG. 9 and Table 1. TABLE1 Eval- Low Surface Contact Coeffi- Car- uation reflectivity regi- angleof cient of Humidity bon: item region stance surface dynamic resistancesili- Sample nm Ω/□ Degrees friction test con Ex. 1 415-705 63 113 0.80No change 0 Ex. 2 420-720 65 112 0.80 No change 0.1 Ex. 3 420-720 64 1140.79 No change 0 Ex. 4 435-700 122  112 0.80 No change 0 Comp. 430-70063  33 1.23 Separated* 0 Ex. 1 Comp. 390-700  10¹⁵  31 1.32 Separated* 0Ex. 2 Comp. 450-710 66  30 1.23 No change 0 Ex. 3 Comp. 525-580 64  341.33 No change 0 Ex. 4

[0117] The anti-reflection film 10 of the present invention comprises ahard coat layer, an intermediate refractive index layer, a highrefractive index layer and a low refractive index layer formed in thissequence on a base film. The hard coat layer is formed from athermosetting or ionizing radiation curing resin. Thus, ananti-reflection film with firm, stable-adhesion of the layers to thebase film and having excellent anti-glare properties can be provided.

[0118] Furthermore, the refracting layers of the anti-reflection filmsof Examples 1 and 2 are composed of three layers. Nevertheless, theseanti-reflection films give an anti-reflection effect comparable to thatof the four-layer product of Comparative Example 2, and they areadvantageous in that the number of steps can be decreased compared withthe four-layer product.

1. An anti-reflection film having an intermediate refractive indexlayer, a high refractive index layer and a low refractive index layerformed in this order on a transparent base film via a hard coat layer,said anti-reflection film comprising: the low refractive index layercomprising an SiO_(X) layer; the intermediate refractive index layerconstituted by a coating of a composition comprising a binder andultrafine particles having a refractive index of 1.5 or more; and thehigh refractive index layer; and said anti-reflection film having: therelationship 2.20>refractive index of the high refractive indexlayer>refractive index of the intermediate refractive indexlayer>refractive index of the low refractive index layer>1.40; thethickness of each refractive index layer being 80 to 110 nm for the lowrefractive index layer, 30 to 110 nm for the high refractive indexlayer, and 50 to 100 nm for the intermediate refractive index layer; andan optical film thickness D not larger than the wavelength of visiblelight (D=n·d wherein n is the refractive index of the intermediaterefractive index layer and d is the thickness of the intermediaterefractive index layer).
 2. An anti-reflection film as claimed in claim1 , wherein the hard coat layer has irregularities on its surface incontact with the intermediate refractive index layer.
 3. Ananti-reflection film as claimed in claim 1 , wherein the hard coat layeris provided on the transparent base film directly or via a primer layerand/or an adhesive layer.
 4. An anti-reflection film as claimed in claim1 , wherein the intermediate refractive index layer comprises 1 part byweight of a thermosetting resin and/or an ionizing radiation curingresin and 0.1 to 20 parts by weight of ultrafine particles of one ormore kinds selected from the group consisting of ultrafine particles ofZnO, TiO₂, CeO₂, Sb₂O₅, SnO₂, ITO, Y₂O₃, La₂O₃, Al₂O₃, Hf₂O₃ and ZrO₂.5. An anti-reflection film as claimed in claim 1 , wherein the highrefractive index layer and the low refractive index layer are each alayer provided by vacuum coating.
 6. An anti-reflection film as claimedin claim 1 , wherein the low refractive index layer is formed by plasmaCVD involving the discharge of the starting gas of an organosiloxane,and the undecomposed organosiloxane remains in an amount of 0.1 to 0.2part based on the silicon.
 7. An anti-reflection film as claimed inclaim 1 , wherein an antifouling layer may be formed on the lowrefractive index layer.
 8. A process for preparation of ananti-reflection film having a hard coat layer, an intermediaterefractive index layer, a high refractive index layer, and a lowrefractive index layer formed in this sequence on a transparent basefilm, comprising the steps of: forming an uncured hard coat layer on atransparent base film; forming an uncured intermediate refractive indexlayer on the transparent base film, said uncured intermediate refractiveindex layer comprising a composition containing a binder and fineparticles having a higher refractive index than the refractive index ofthe binder; laminating a mirror-shaped or finely irregular, mattedshaped film on the uncured intermediate refractive index layer to shapethe surface of the intermediate refractive index layer; heat-treatingand/or ionizing radiation treating the resulting laminate to cure theuncured layers; removing the shaped film from the cured laminate to forman intermediate refractive index layer having a smooth or finelyirregular surface on the transparent base film; forming a highrefractive index layer on the intermediate refractive index layer byvacuum deposition or sputtering; and forming a low refractive indexlayer comprising an SiO_(X) layer on the high refractive index layer byvacuum deposition, sputtering or plasma CVD.
 9. A process forpreparation of an anti-reflection film having a hard coat layer, anintermediate refractive index layer, a high refractive index layer, anda low refractive index layer formed in this sequence on a transparentbase film, comprising the steps of: forming an uncured intermediaterefractive index layer on a mirror-shaped or matted shaped film havingirregularities on the surface, said uncured intermediate refractiveindex layer comprising a composition containing a binder and fineparticles having a higher refractive index than the refractive index ofthe binder; laminating the uncured intermediate refractive index layerto an uncured hard coat layer provided on a transparent base film;heat-treating and/or ionizing radiation treating the resulting laminateto cure the uncured layers; stripping off the shaped film from the curedlaminate to form an intermediate refractive index layer having a smoothor finely irregular surface on the transparent base film; forming a highrefractive index layer on the intermediate refractive index layer byvacuum deposition or sputtering; and forming a low refractive indexlayer comprising an SiO_(X) layer on the high refractive index layer bysputtering or plasma CVD.
 10. A process for preparation of ananti-reflection film having an intermediate refractive index layer, ahigh refractive index layer, and a low refractive index layer formed inthis sequence on a transparent base film via a hard coat layer,comprising the steps of: coating a shaped film having a mirror- ormat-shaped surface with an uncured intermediate refractive index layercontaining a binder and fine particles having a higher refractive indexthan the refractive index of the binder, and an uncured hard coat layer,followed by curing, to form an intermediate refractive index layer and ahard coat layer; laminating an uncured surface of a reactive adhesivelayer coated on a transparent base film to the cured hard coat layer;heat-treating and/or ionizing radiation treating the resulting laminateto cure the adhesive layer; stripping off the shaped film from the curedlaminate to form the intermediate refractive index layer having a smoothor irregular surface and the hard coat layer on the transparent basefilm; forming a high refractive index layer on the intermediaterefractive index layer by vacuum deposition or sputtering; and forming alow refractive index layer comprising an SiO_(X) layer on the highrefractive index layer by sputtering or plasma CVD.
 11. Ananti-reflection film as claimed in claim 1 , wherein the high refractiveindex layer comprises a sputter film of ITO, and its surface resistanceis 10³Ω/¤ or less.
 12. An anti-reflection film as claimed in claim 1 ,wherein the binder of the intermediate refractive index layer comprisesa thermosetting and/or ionizing radiation curing organosilicon compound.13. An anti-reflection film as claimed in claim 1 , wherein theultrafine particles of the intermediate refractive index layer compriseZrO₂ particles.
 14. An anti-reflection film having an intermediaterefractive index layer, a high refractive index layer and a lowrefractive index layer formed in this sequence on a transparent basefilm via a hard coat layer, said anti-reflection film comprising: thelow refractive index layer comprising an SiO_(X) layer; the intermediaterefractive index layer constituted by coating a paint comprising abinder and ultrafine particles having a refractive index of 1.5 or more;and the high refractive index layer having electric conductivity; andsaid anti-reflection film having: the relationship 2.20>refractive indexof the high refractive index layer>refractive index of the intermediaterefractive index layer>refractive index of the low refractive indexlayer>1.40; and the ultrafine particles of the intermediate refractiveindex layer comprising ZrO₂ particles.
 15. An anti-reflection film asclaimed in claim 1 , wherein the high refractive index layer haselectric conductivity.